1. Field of the Invention
The present invention relates, in general, to a non-contact photoplethysmographic pulse measurement device, and oxygen saturation and blood pressure measurement devices using the non-contact photoplethysmographic pulse measurement device, and, more particularly, to a non-contact photoplethysmographic pulse measurement device, and oxygen saturation and blood pressure measurement devices using the non-contact photoplethysmographic pulse measurement device, which can measure a photoplethysmographic pulse, oxygen saturation and an electrocardiogram without making direct contact with a user's skin while the user is unaware of the measurement being taken, and can measure blood pressure using both the photoplethysmographic pulse and the electrocardiogram.
2. Description of the Related Art
Whenever the heart is contracted, blood is supplied from the heart to the whole body through the main artery, and, at this time, variation in pressure occurs in the main artery. Such variation in pressure is transferred up to the peripheral arterioles of the hands and feet. The term ‘photoplethysmographic (PPG) pulse’ means a pulse wave representing variation in the volume of peripheral blood vessels, attributable to variation in the internal pressure of the artery.
The volume of a blood vessel changes due to such a pulsation. When light having a certain wavelength such as infrared light or visible light is provided to a blood vessel, the volume of the blood vessel increases or decreases, and thus the amount of light absorbed by the blood vessel changes. For example, when light of 100 is emitted, the amount of light which is reflected and is not absorbed may change following the beat of the pulse.
On the basis of this principle, after light is emitted through a light emitting unit, the speed or amount of reflected infrared light is input to a light receiving unit, and then a photoplethysmographic (PPG) pulse can be measured using the characteristic that current and voltage vary according to the speed or amount of input infrared light.
A conventional PPG pulse measurement device performs measurement by bringing a sensing unit into contact with the skin so as to measure a PPG pulse. Accordingly, there is a disadvantage in that the skin must always be maintained in a clean state, and an examinee must assume a peaceful attitude so that his or her mental state does not influence the waveform of the pulse wave.
In order to overcome this disadvantage, a non-contact PPG pulse measurement device, which is capable of measuring a PPG pulse through the clothing of a user without making direct contact with the skin while the user is unaware of the measurement being taken, is required.
To measure a PPG pulse through clothing, light, which is emitted from a light emitting unit, must be able to pass through the clothing and enter the skin tissue and the artery, and light, which is not absorbed and is reflected, must pass through the clothing and reach a light receiving unit. For this operation, it is necessary to emit light with a higher luminance than that of light used at the time of measuring a PPG pulse on the skin such as is used in the case of the conventional technology.
As shown in FIGS. 9A to 9B, the sensing unit of a conventional PPG pulse measurement device is configured such that one light emitting unit 10, implemented using a Light Emitting Diode (LED), and one light receiving unit 20, implemented using a photodetector, are arranged in parallel with each other. Meanwhile, since the LED radiates light in a circular pattern, only part of the light reflected from the tissue of a human body is incident on a sensing area of the light receiving unit 20. That is, there is a problem in that, of a total amount of reflected light, a large amount of that light is not sensed by the light receiving unit 20. Therefore, the revision of the sensing unit is required to emit high-luminance light.
Meanwhile, since light emitted with high luminance causes the saturation of signals, a PPG pulse measurement device capable of emitting light having suitable luminance according to the thickness of clothing is required.